How to make query that find inside of find in mongodb - mongodb

Question

I have a document as below in Mongodb.
{
"vatInfo":{
"company": "apple"
},
"type": "manager",
"parent": "123"
}
And I have another document in same collection as below.
{
"type": "member",
"parentId": "123",
"id": "3"
}
And when I make client.find({id: 3, type: 'member'}), I want to get this that finds vatInfo automatically inside of find.
{
"type": "member",
"parentId": "123",
"id": "3",
"vatInfo":{
"company": "apple"
},
}
How should I make aggregate for this find? I dont want to make double find.
Thank you so much for reading it.

Answer 1

You can use the aggregation pipelines for that.
$match - find the parent documen.
$lookup - join the document from the other collection.
$project - modify the structure of the result.
// collection `client`
{
"vatInfo":{ "company": "apple" },
"type": "manager",
"parent": "123"
},
{
"type": "member",
"parentId": "123",
"id": "3"
}
// query example
db.getCollection('client').aggregate([
{ $match: { 'id': '3', 'type': 'member' } },
{
$lookup: {
from: 'client',
localField: 'parentId',
foreignField: 'parent',
as: 't01'
}
},
{
$project: {
'_id': 0,
'type': 1,
'parentId': 1,
'id': 1,
'vatInfo': { $arrayElemAt: [ "$t01.vatInfo", 0 ] }
}
}
])
// result
{
"type" : "member",
"parentId" : "123",
"id" : "3",
"vatInfo" : {
"company" : "apple"
}
}

Answer 2

To add the field of another document, you can use populate in Mongoose :
For this to work you need to have a reference in your schema between the client document and the parent document :
const clientSchema = Schema({
[...]
parentId: { type: Schema.Types.ObjectId, ref: 'ParentCollection' }
});
Then, you can use populate anywhere in your code :
client.findOne({id: 3, type: 'member'}).populate('parentId');